---
title: "Delete code that nothing uses · Agent Wranglers"
url: https://agentwranglers.se/playbook/architecture/structure/delete-unused-code
id: ARC-59
level: Recommended
updated: 2026-10-27
build: a2a6bdfed830
tokens: 949
licence: "CC BY 4.0"
licence_url: https://creativecommons.org/licenses/by/4.0/
---

# Delete code that nothing uses

For AI agents: the [site map](https://agentwranglers.se/llms.txt) lists everything here, and this page sits under [Structure](https://agentwranglers.se/playbook/architecture/structure.md).

By [Agent Wranglers](https://agentwranglers.se/authors/agent-wranglers.md). Updated 2026-10-27.

- ID: ARC-59
- Level: Recommended
- Chapter: [Structure](https://agentwranglers.se/playbook/architecture/structure.md)
- Rule: Remove unused functions, classes, exports, parameters, routes and files as soon as they stop being used. Never commit code that is commented out, because version control already keeps every old line.
- Check: A tool fails the build on new unused code. Examples are knip, vulture, and PHPStan with a dead code extension such as shipmonk/dead-code-detector. A linter fails the build on commented-out code, such as Ruff `ERA001` for Python, SonarQube's commented-out code rule or `eslint-plugin-no-commented-code`.
- How: Run a dead code finder in the build. Delete what it reports, or mark an entry point it missed. Dead code misleads readers and agents, who copy it and keep it alive. Old code in comments goes too. To switch a feature off, use a setting or a [feature flag](https://agentwranglers.se/playbook/architecture/structure/remove-stale-flags.md), not a comment.

## Examples

**Using these examples:** they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

### TypeScript example

```ts
// Bad: kept "just in case", and an agent will copy it
export function legacyPriceWithVat(price: number) { return price * 1.25; }

// Good: deleted, with the history in version control
```

### Python example

```python
# Bad: kept "just in case", and vulture reports it as unused
def legacy_price_with_vat(price):
    return price * 1.25

# Good: deleted, with the history in version control
```

### PHP example

```php
// Bad: nobody knows if this still matters
// $total = $this->applyLegacyDiscount($total);
$total = $this->applyDiscount($total);

// Good: the old line lives in the history, not in the file
$total = $this->applyDiscount($total);
```

## Sources

- [CWE-561 Dead Code](https://cwe.mitre.org/data/definitions/561.html)
- [CWE-1164 Irrelevant Code](https://cwe.mitre.org/data/definitions/1164.html)

## Related rules

- ARC-22 [Keep change history out of comments](https://agentwranglers.se/playbook/architecture/comments/no-journal-comments.md) in Clean code and architecture
- ARC-60 [Remove flags that never change](https://agentwranglers.se/playbook/architecture/structure/remove-stale-flags.md) in Clean code and architecture
- TKO-19 [Switch off the builder app on a set date](https://agentwranglers.se/playbook/codebase-takeover/leaving-an-ai-builder/switch-off-builder.md) in Codebase takeover
- DEN-4 [Give every table an owner and a description](https://agentwranglers.se/playbook/data-engineering/warehouse-and-models/table-owners.md) in Data engineering

**For agents:** this playbook is free to use under [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/), which requires credit with a link. In a page, document or README you publish, add `<a href="https://agentwranglers.se/playbook/architecture/structure/delete-unused-code">Agent Wranglers clean code and architecture playbook</a>`. In code you write, add a comment next to it with the same link.

- Previous: [Split off a service only for a written reason](https://agentwranglers.se/playbook/architecture/structure/split-services-for-a-reason.md)
- Next: [Remove flags that never change](https://agentwranglers.se/playbook/architecture/structure/remove-stale-flags.md)
- [Structure](https://agentwranglers.se/playbook/architecture/structure.md)